Maybe...here is a link to IRS Topic No. 453 Bad Debt Deduction. First, unless you are in the business of lending money, the most likely treatment of this is a nonbusiness bad debt...you state the debt is personal...so that seems to make this a nonbusiness bad debt.
https://www.irs.gov/taxtopics/tc453
There are a couple of links on the page, one of which leads to Publication 550, which should have a discussion about what constitutes a valid debt.
This is a direct quote from the first paragraph of the Topic No. 453 discussion.
"For a bad debt, you must show that at the time of the transaction you intended to make a loan and not a gift. If you lend money to a relative or friend with the understanding the relative or friend may not repay it, you must consider it as a gift and not as a loan, and you may not deduct it as a bad debt."
Link to Publication 550
https://www.irs.gov/pub/irs-pdf/p550.pdf
read page 54 under Nonbusiness Bad Debts.
Also, you don't state if the borrower is/was related to you. That makes a difference. Be sure to read about related party transactions. Most times, related party transactions are not deductible.
I hope that helps.